1. Field of the Invention
The present invention generally relates to radio communication apparatuses, and more particularly to a radio communication apparatus which subjects each signal which is received via a multi-path and demodulated, to a Hadamard transform at each finger, by use of an M-ary quadrature coding scheme, obtains correlation values of the codes, combines correlation values output from the fingers which obtain valid correlation values, and demodulates a received signal based on a maximum correlation value of the combined correlation values.
The code division multiple access (CDMA) system is regarded as a mobile communication system of the next generation, and in the United States, a standardized system (N-CDMA) called IS-95 is already reduced to practice. In addition, there is a possibility of the CDMA system being applied to a semi-fixed mobile communication system called wireless local loop (WLL) as a means of infra-structure. Such a system proposed by Qualcomm of the United States is a CDMA system using a chip rate of 1.2288 Mcs, wherein a synchronous detection system using an extrapolated pilot signal is employed for the down-line, and an asynchronous detection system using the M-ary orthogonal modulation is employed for the up-line. In the asynchronous detection system, an amplitude signal is converted into power so as to eliminate a phase error caused by fading or the like, and the communication quality or bit error rate (BER) is improved by employing the RAKE reception technique. The present invention, as will be described later, is suited for application to this kind of radio communication apparatus.
2. Description of the Related Art
FIGS. 1 through 7 and FIGS. 8A through 8C are diagrams for explaining the prior art, more particularly, the standardized system IS-95. FIG. 1 is a system block diagram showing a transmitter part of a mobile station, and FIG. 2 is a diagram showing a signal sequence of the transmitter part. Signals (A) through (E) shown in FIG. 2 are the signals (A) through (E) shown in FIG. 1.
An input information signal is subjected to a cyclic coding in a CRC operation unit 11, and is converted into an error correction code in a convolutional encoder (ENC) 12. This error correction code is subjected to an identical symbol repeating process in a symbol repeating unit 13, so as to unify the input signals in the range of 1.2 kbps to 9.6 kbps to the signal (A) of 9.6 kbps. The signal (A) is further subjected to a buffering process in an interleaver 14. A signal sequence (B) of 28.8 kbps is read from the interleaver 14 and input to an M-ary (64) orthogonal modulator 15.
The 64-ary orthogonal modulator 15 converts the 6-bit input data to a corresponding 64-bit Walsh code (C), that is, spreads the input data by 64/6 times. For example, the 6-bit input data xe2x80x9c000000xe2x80x9d is converted into a 64-bit Walsh code xe2x80x9c00000000 . . . 00000000xe2x80x9d, and the 6-bit input data xe2x80x9c000001xe2x80x9d is converted into a 64-bit Walsh code xe2x80x9c01010101 . . . 01010101xe2x80x9d. Such Walsh codes (C) are finally output from the 64-ary orthogonal modulator 15 as a signal (D) of 307.2 kcps.
A multiplier 17 multiplies to the signal (D) a PN code (user code or long code) LCD which is generated for each user by a long code generator 16. As a result, a spread code sequence (E) of 1.2288 Mcps is output from the multiplier 17 and is supplied to a multiplier 201 provided for the I-channel and a multiplier 202 provided for the Q-channel. The multiplier 201 multiplies to the spread code sequence (E) a PN code (short code) SCD for identifying the base station, which is generated from a short code generator 18 and is received via a shifter 19. On the other hand, the multiplier 202 multiplies to the spread code sequence (E) the PN code SCD which is generated from the short code generator 18.
An output of the multiplier 201 is passed through a filter 221 and a digital-to-analog (D/A) converter 231 and converted into an analog signal before being supplied to a quadrature phase shift keying (QPSK) modulator 24. An output of the multiplier 202 is passed through a xc2xd chip delay unit 21, a filter 222 and a D/A converter 232 and converted into an analog signal before being supplied to the QPSK modulator 24. Since the xc2xd chip delay unit 21 provides a xc2xd chip shift between the I-channel and the Q-channel, an output of the QPSK modulator 24 becomes an offset QPSK (OQPSK) modulated signal. By this OQPSK modulation, no phase change of xcfx80 occurs, and the phase change becomes xcfx80/2 at the maximum. For this reason, even under an extreme band limitation, the signal envelope only dips slightly, and no zero-point occurs. An OQPSK modulated signal output from the QPSK modulator 24 is converted into a radio frequency signal in a transmitting radio frequency (RF) unit (Tx) 25 and is transmitted to the base station via an antenna A0.
FIG. 3 is a system block diagram showing a receiver part (reverse link demodulator part) of the base station. In addition, FIG. 4 is a diagram for explaining a service area of the base station, and FIG. 5 is a diagram for explaining asynchronous detection. Further, FIG. 6 is a system block diagram showing fingers forming the receiver part, and FIG. 7 is a diagram showing a signal sequence of the receiver part.
As shown in FIG. 4, 1 cell is divided into 3 sectors, and 2 reception (diversity) antennas are provided with respect to 1 sector. A maximum number of antennas capable of simultaneously communicating with a mobile station MS which is located at an arbitrary position is 4, namely, A11, A12, A21 and A22, in this particular case. Hence, 4 corresponding antennas A1 through A4 are shown in FIG. 3.
In FIG. 3, the received signals from the antennas A1 through A4 are amplified and converted into intermediate frequency signals IF in corresponding receiving RF units (Rx) 311 through 314, and demodulated into orthogonal demodulated data (I1, Q1) through (I4, Q4) in corresponding QPSK demodulators (DEM) 321 through 324. The orthogonal demodulated data (I1, Q1) through (I4, Q4) are selected by a signal selector 33 which operates under the control of a searcher 40, and input to fingers 341 through 344. In this state, the received wave is not necessarily supplied constantly to each finger, and each finger operates under conditions, such as antenna selection and delay time PNoffset, which are specified by the searcher. Hence, various combinations are actually permitted for the connection of the QPSK demodulators 321 through 324 and the fingers 341 through 344.
FIG. 6 shows the construction of the fingers 341 through 344. In a despreader 41 of the finger 341, the input demodulated data I1, Q1 are respectively despread by a correlator 42 based on the short code PNoffset (PNI1, PNQ1) supplied from the searcher 40. The short codes PNI1, PNQ1 correspond to the short code SCD of the transmitter end, and PNI1 is phase (chip) synchronized to the demodulated data I1 while PNQ1 is phase (chip) synchronized to the demodulated data Q1.
Further, output data I1, Q1 of the correlator 40 are despread by corresponding multipliers 431 and 432 based on a long code LCD corresponding to the user code LCD of the transmitting end. In addition, an adder 441 adds 4 consecutive despread codes I1 from the multipliers 431, and an adder 442 adds 4 consecutive despread codes Q1 from the multiplier 432. If no chip error occurs during the transmission, output data I1, Q1 (A) of the adders 441 and 442 correspond to the output Walsh code of the 64-ary orthogonal modulator 15 of the transmitting end. Actually, however, the output data I1, Q1 (A) of the adders 441 and 442 do not necessarily correspond to the output Walsh code of the 64-ary orthogonal modulator 15 due to the chip error or the like introduced during the transmission.
The output data I1, Q1 (A) of the adders 441 and 442 are subjected to the Hadamard transform in corresponding fast Hadamard transform units (FHT) 451 and 452. In other words, the input data I1, Q1 and 64 kinds of Walsh code sequences are subjected to matrix operations, so that correlation values (I00 through I63), (Q00 through Q63) are generated depending on the correlation of the codes. Energy calculation units 4600 through 4663 obtain powers (I002+Q002) through (I632+Q632) for each of the correlation values, and output correlation energies E00 through E63 corresponding to Walsh code numbers 0 through 63.
The correlation energies E00 through E63 are input to a gate circuit 47 and to a maximum value selector (MXS) 48. The maximum value selector 48 selects a maximum correlation energy MXE from the correlation energies E00 through E63. A comparator (CMP) 49 compares the maximum correlation energy MXE and a predetermined threshold value TH, and closes the gate circuit 47 when MXE greater than TH and otherwise opens the gate circuit 47. In other words, the output correlation energies E00 through E63 of the energy calculation units 4600 through 4663 are output from the finger 341 and contribute to the RAKE combining at the latter stage only when the maximum energy MXE exceeds the predetermined threshold value TH. Similar operations are carried out in the other fingers 342 through 344. Under the RAKE reception system, the correlation value level is made large by combining only the correlation value outputs from the valid fingers of each of the correlation value outputs (energies) of the multi-path which includes 4 paths at the maximum in FIG. 3, so as to increase the certainty of the correlation value.
Returning now to the description of FIG. 3, the output correlation energies E00 through E63 from the fingers 341 through 344 are combined (added) for each of the correlation energies E00 through E63 in the combining units 3500 through 3563, and combined energies G00 through G63 are output from the combining units 3500 through 3563. A maximum value selector 36 selects a maximum combined energy MXG of the combined energies G00 through G63, and demodulates a Walsh code (number) MXW corresponding to this maximum combined energy MXG. Under the asynchronous detection system, the phase component is eliminated by converting the demodulated signals I, Q into power (I2+Q2), so as to prevent phase noise caused by fading and to prevent deterioration of a local signal caused by frequency error. FIG. 5 is a diagram for explaining the asynchronous detection in this state. Even if the demodulated phase changes (rotates) by xcex94xcfx86 between timings t1 and t2, the maximum combined energy MXG=G15 is obtained at the timing t1, and the maximum combined energy MXG=G32 is obtained at the timing t2. The Walsh code MXW is converted into a corresponding 6-bit data by a code converter 37, deinterleaved in a deinterleaver 38, subjected to a Viterbi decoding in a Viterbi decoder 39, and output as received data RD.
According to the conventional system described above, the finger locked state occurs when MXE greater than TH as a result of the comparison of the maximum combined energy MXE of the combined energies G00 through G63 and the predetermined threshold value TH.
FIG. 8A is a diagram showing an example of a correlation energy versus Eb/No characteristic. In FIG. 8A, the ordinate indicates the correlation energy, and the abscissa indicates Eb/No, that is, the signal-to-noise (S/N) ratio per bit. Generally, the correlation energy is high when Eb/No (reception quality) is high, and the correlation energy decreases when Eb/No decreases, as will be described hereunder.
FIG. 8B is a diagram showing an example of a case where Eb/No is sufficiently high. In FIG. 8B, the ordinate indicates the correlation energy, and the abscissa indicates energy types E00 through E63 corresponding to the Walsh code numbers W00 through W63. If Eb/No (communication quality) is sufficiently high and the Walsh code W15 sent from the transmitting end is correctly demodulated into the code W15 at the receiving end, the correlation energy E15 becomes MXE at the maximum, and the other correlation energies all become xe2x80x9c0xe2x80x9d. Accordingly, the conventional system can accurately judge whether or not XXE greater than TH1.
FIG. 8C is a diagram showing an example of a case where Eb/No decreases. In FIG. 8B, the ordinate indicates the correlation energy, and the abscissa indicates energy types E00 through E63 corresponding to the Walsh code numbers W00 through W63. If Eb/No (communication quality) decreases, burst error or the like mixes into the Walsh code W15 sent from the transmitting end, and the correlation energy E15 decreases in a received code W15xe2x80x2 which includes error and is demodulated at the receiving end. As a result, the correlation energy increases in relation to the other codes, and in the conventional system it is impossible to detect whether or not E15 greater than TH1, that is, whether or not the finger locked state occurs.
In this case, if the threshold value TH1 is decreased to a threshold value TH2, it is possible to detect the finger locked state. However, as may be seen from FIG. 8C, a correct RAKE combining operation cannot be expected by outputting (locking) fingers for which a sufficiently accurate judgement cannot be made to determine which one of the energies E15 and E45 is larger. Hence, according to the conventional system, a necessary finger may be disabled or an unnecessary finger may be enabled when Eb/No decreases, thereby deteriorating the reception quality. In addition, it is difficult to set the threshold value TH so as to improve the reception quality.
Moreover, in mobile communication systems in general, the transmission power of the mobile station MS is remotely controlled so that Eb/No obtained after combining the fingers becomes a desired value. For this reason, as the number of fingers which are combined becomes large, Eb/No per finger may decrease accordingly, thereby making it more difficult to detect the finger locked state for each of the fingers.
Furthermore, in this type of communication system, the fingers are arranged depending on an instruction from the searcher 40. But in the conventional system, even in a case where a plurality of fingers receive identical or extremely similar signals, these fingers will assume the finger locked state together, and the fingers will be combined in this state.
However, there is virtually no gain in the RAKE reception even if identical signals are combined, and the plurality of fingers will be used in vain. In addition, the number of fingers actually being combined and the number of fingers substantially contributing to the RAKE combining do not match. Consequently, undesirable effects are introduced to other controllers, such as a remote control to decrease the transmission power of the mobile station MS.
Accordingly, it is a general object to provide a novel and useful radio communication apparatus in which the problems described above are eliminated.
Another and more specific object of the present invention is to provide a radio communication apparatus which can always appropriately combine fingers (RAKE) depending on the communication environment and the location of the terminal station.
Still another object of the present invention is to provide a radio communication apparatus which subjects each signal which is received via a multi-path and demodulated, to a Hadamard transform at each of fingers, by use of an M-ary quadrature coding scheme, obtains correlation values of codes, combines correlation values output from fingers which obtain valid correlation values, and demodulates a received signal based on a maximum correlation value of combined correlation values, where the radio communication apparatus comprises an operation unit which obtains a difference between a maximum value and a second largest value of the correlation values of a corresponding one of the fingers, and a lock controller which enables and locks the correlation values output from the corresponding one of the fingers when the difference obtained by the operation unit is greater than or equal to a predetermined value. According to the radio communication apparatus of the present invention, it is possible to always obtain an appropriate combining of the fingers (RAKE) depending on the communication environment and the location of the terminal station, and the communication quality is improved.
A further object of the present invention is to provide radio communication apparatus which subjects each signal which is received via a multi-path and demodulated, to a Hadamard transform at each of fingers, by use of an M-ary quadrature coding scheme, obtains correlation values of codes, combines correlation values output from fingers which obtain valid correlation values, and demodulates a received signal based on a maximum correlation value of combined correlation values, where the radio communication apparatus comprises a maximum value detector which obtains a maximum correlation value of a corresponding one of the fingers, a combining unit which combines, at a predetermined ratio, the maximum correlation value obtained by the maximum value detector and a maximum correlation value obtained after combining the fingers, and a lock controller which enables and locks output of the correlation values from the corresponding one of the fingers when an output of the combining unit is greater than or equal to a predetermined value. According to the radio communication apparatus of the present invention, it is possible to always obtain an appropriate combining of the fingers (RAKE) depending on the communication environment and the location of the terminal station, and the communication quality is improved.
Another object of the present invention is to provide a radio communication apparatus which subjects each signal which is received via a multi-path and demodulated, to a Hadamard transform at each of fingers, by use of an M-ary quadrature coding scheme, obtains correlation values of codes, combines correlation values output from fingers which obtain valid correlation values, and demodulates a received signal based on a maximum correlation value of combined correlation values, where the radio communication apparatus comprises a maximum value detector which obtains a maximum correlation value of a corresponding one of the fingers, a code generator which generates an M-ary quadrature code corresponding to the maximum correlation value of the corresponding one of the fingers, a comparator which compares the M-ary quadrature code generated by the code generator and an M-ary quadrature code corresponding to the maximum correlation value obtained after combining the fingers, a selector which selects the maximum correlation value of the corresponding one of the fingers or a predetermined coefficient multiple thereof when no match is detected by the comparator, and selects the maximum correlation value obtained after combining the fingers or a predetermined coefficient multiple thereof when a match is detected by the comparator, and a lock controller which enables and locks output of the correlation values from the corresponding one of the fingers when an output of the selector is greater than or equal to a predetermined value. According to the radio communication apparatus of the present invention, it is possible to always obtain an appropriate combining of the fingers (RAKE) depending on the communication environment and the location of the terminal station, and the communication quality is improved.
Still another object of the present invention is to provide a radio communication apparatus which subjects each signal which is received via a multi-path and demodulated, to a Hadamard transform at each of fingers, by use of an M-ary quadrature coding scheme, obtains correlation values of codes, combines correlation values output from fingers which obtain valid correlation values, and demodulates a received signal based on a maximum correlation value of combined correlation values, where the radio communication apparatus comprises a comparator which compares demodulate data for an arbitrary combination of 2 paths, and a lock controller which disables and unlocks output of the correlation values from a corresponding one of the fingers based on a detection of a match or an approximate match in the comparator. According to the radio communication apparatus of the present invention, it is possible to always obtain an appropriate combining of the fingers (RAKE) depending on the communication environment and the location of the terminal station, and the communication quality is improved.
A further object of the present invention is to provide a radio communication apparatus which subjects each signal which is received via a multi-path and demodulated, to a Hadamard transform at each of fingers, by use of an M-ary quadrature coding scheme, obtains correlation values of codes, combines correlation values output from fingers which obtain valid correlation values, and demodulates a received signal based on a maximum correlation value of combined correlation values, where the radio communication apparatus comprises a comparator which compares M-ary quadrature codes corresponding to maximum correlation values obtained for an arbitrary combination of 2 fingers, and a lock controller which disables and unlocks output of the correlation values from one of the 2 fingers when a match is detected by the comparator. According to the radio communication apparatus of the present invention, it is possible to always obtain an appropriate combining of the fingers (RAKE) depending on the communication environment and the location of the terminal station, and the communication quality is improved.